1. Field of the Invention
The invention concerns methods, apparatus, and systems for a wireless transceiver with receive and transmit path performance diversity.
2. Related Art
Wireless communication devices typically operate in many different signal environments. Some operating environments permit high quality communication links supporting high data rates at relatively low transmit powers, while other environments permit only marginal quality communication links using relatively low data rates and requiring relatively high transmit powers. In other embodiments, a wireless communication device may utilize a high transmit power in order to support high data rates, or may support a low data rate at a relatively low transmit power.
The operating environment experienced by a wireless communication device may be largely determined by natural phenomena, such as the proximity of participants in a communication link, terrain, obscurations, weather conditions, and the like. Operating environments may also be largely affected by man-made phenomena, such as interference sources, spurious emissions, unintentional jammers, and the like.
The spectral proximity of the operating frequency band of the wireless communication device to frequency bands having potentially large interference sources can be used in estimating the potential adverse effects attributable to the out of band interference sources. Unfortunately, the operating frequency band of the wireless communication device may not be contiguous, and may be interrupted by one or more bands having potentially large interference sources. A receive front end in a wireless communication device typically spans the entire operating band. Even if multiple receive front end portions are aggregated to support an entire operating band, typically at least one front end portion is responsive to signals from an out of band interference source in a band adjacent to the operating frequency band. A front end device that is responsive to out of band interference source may operate with degraded performance in the presence of the out of band interference source. For example, an amplifier may be driven to a nonlinear mode in the presence of a strong out of band interference source.
The ability of a wireless communication device to filter out or otherwise attenuate potential large interference sources depends upon the design margins available for the receiver. Front end filters used to reject out of band interference sources typically introduce attenuation in the desired pass band. Typically, cascading multiple filters to provide rejection of all potential out of band interference sources results in the introduction of a substantial amount of attenuation into the receive front end. Increasing the amount of attenuation in a receive front end is typically not desirable, as it increases the noise figure of the receiver and reduces the corresponding receiver sensitivity.
However, providing substantially no filtering of out of band interference sources exposes the receiver in the wireless communication device to the out of band interference sources. An out of band interference source having substantially larger transmit power than a desired signal can operate, in essence, as a jammer.
An out of band jammer signal can cause a gain control loop within the receiver to reduce the gain applied to receive signals, which can desensitize the receiver to desired signals. Furthermore, an out of band jammer signal can result in the receive front end being driven to a nonlinear state. The large jammer signal can effectively capture the receiver making it virtually useless for receiving the desired signal. The receive front end can generate substantial distortion products, including potentially in band intermodulation distortion products when operated in the nonlinear state. The in-band distortion products cannot be removed using conventional filtering.
A transmitter portion of the wireless communication device operates under similar but complementary constraints. The out of band emissions from the transmitter portion may be constrained over the entire operating range of the transmitter.
The design of the wireless communication device may be further complicated in wireless communication devices that time division duplex transmit and receive portions over a shared RF path. In such a device, the filtering implemented to satisfy the out of band transmit emissions constraints may adversely affect the sensitivity of the receiver portion. Similarly, filtering introduced to alleviate effects of out of band interference sources on the receiver portion may introduce additional attenuation into the transmit path resulting in a substantial loss of transmit power.
Therefore, it is desirable to control the effects of out of band interference sources on a receiver while maintaining the out of band emissions constraints on a transmitter.